A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
The marker that you see marks the bottom right corner of a table. If you click that cell, then click on the Table Tools ribbon and select a different table style, you can see where the table starts and ends.
Armed with that information you now know: You have a table in your worksheet that goes from (probably) column A to column G. When you sort, the sort gets applied to the columns in the table. The columns H and following are outside of the table and will not be include in the sort.
You can include more columns and rows into an existing table like this: with a cell in the table selected, click the Table Tools ribbon. On the very left of the ribbon click the command "Resize Table. Select all rows and columns that you want to include in the table and hit OK.